Conventionally, vehicle doors comprise a supportive inner panel made of steel material. An outer panel is attached to the inner panel. The conventional inner panel is deep-drawn from mild steel. A beltline beam beneath the window is welded to the inner panel and can be placed either inwardly of or outwardly of the window. Typically, the vehicle doors include a generally horizontally extending side impact guard beam made of steel that has a considerably higher mechanical strength than the steel from which the inner panel is made. The impact guard beam is welded to the inner panel and placed nearest the outer panel. A relatively flat trim is fastened to the inner panel. The inner door components, such as locks, window guides and window elevators, are mounted to the inner panel.
Furthermore, steel sheet has been the most widely used raw material for motor vehicle doors. Steel doors are inexpensive and simple to manufacture. However, conventional steel door designs are relatively heavy in comparison to the mass of newly designed aluminum doors. Accordingly, there is a tendency in the automotive industry to replace steel doors with the doors made of aluminum. The aluminum doors, although lighter than conventional steel doors, are however costlier than steel doors and more complex, difficult and expensive to manufacture.
Therefore, vehicle doors made of steel are susceptible to improvements that may enhance their performance, cost and weight. With this in mind, a need exists to develop an improved vehicle door made of high-strength steel with reduced weight comparable to that of the weight of aluminum doors, improved performance, and inexpensive to manufacture.